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D.M. Richiert, X. Zhu, J.R. Mertz, J. Wallman; Choroidal retinoic acid synthesis reflects sign of defocus. . Invest. Ophthalmol. Vis. Sci. 2004;45(13):1236.
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Purpose: In both chicks and monkeys, positive and negative lenses have opposite effects on eye growth. Several signal molecules also show opposite responses to lenses of opposite sign. In particular, the rate of synthesis of retinoic acid by the choroid is increased by positive lenses and decreased by negative lenses. Is this difference a reflection of the lenses imposing opposite signs of defocus or differences in the amount of sharp vision? We had chicks wear positive or negative lenses briefly while confined in a drum, the walls of which were beyond their far–point when wearing positive lenses. Methods: Chicks wore +10 or –7 D lenses over one eye for 15 minutes four times in a single day and were kept in the dark between episodes. Changes in refraction and choroidal thickness were measured by Hartinger refractometry and A–scan ultrasonography, respectively. Choroids were incubated with radioactive retinol for 90 minutes. Retinoic acid was separated by normal phase HPLC and quantified by scintillation counting. Results: All 10 birds wearing positive lenses had higher rates of synthesis of retinoic acid in the lens–wearing eye (mean 42±12% difference; p<0.001). These eyes were 1.5 D more hyperopic than their fellow eyes (p<0.05) and had choroids that were 60 µm thicker (p<0.01). All 5 birds wearing negative lenses had lower rates of synthesis of retinoic acid in the lens–wearing eye (mean 22±8% difference; p<0.001). These eyes were 1.0 D more myopic than their fellow eyes but had no significant choroidal thinning. Overall the retinoic acid was not correlated with choroidal thickness. Conclusions: Positive lenses increase choroidal synthesis of retinoic acid even when sharp vision was eliminated. Negative lenses cause decreased choroidal retinoic acid synthesis even when worn for too little time to cause changes in choroidal thickness. These findings support the existence of sign–dependent modulation of eye–growth by retinoic acid.
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